The Columbia University Radiological Research Accelerator Facility (RARAF) is a user-friendly facility dedicated to radiobiological research with particulate ionizing radiations such as alpha particles and neutrons. Our overall goal in this Resource Grant is development and application of two new facilities based on the RARAF accelerator. Continued development is proposed of a microbeam facility which delivers a predetermined number of charged particles (from 1 upward) in a given location through each of a number of cells growing on a dish. The first goal is to attain a maximum throughput of 5-10,000 cells/h, and a maximum precision of +/- 1.5 um; the second goal is to develop new optical cell-location imaging systems, including facilities for locating cells without use of stain and UV exposure; the third goal is to extend the maximum radiation stopping power (LET) that can be used, and the final goal is to develop appropriate biological protocols for optimal use of the facility. It is also proposed to develop a series of well-defined low-energy neutron beams (lowest dose-averaged mean energy <30 keV) for biological research. This technological development is based on a proton beam incident on a rotating lithium target. Techniques will be developed for micro- and nano-dosimetric characterization of these low-energy neutron beams. The final goal here, as with the microbeam, is to develop appropriate biological protocols to allow optimal use of the low-energy neutron facility. In collaboration with a variety of investigators from within and outside Columbia University, twenty collaborative and service-based research projects are described, based on funded research programs, which both drive and utilize the new resources. Training and information dissemination will be important components of this resource, both through visiting scientists, students, organized workshops, and written and electronically accessible user information.